Wireless handoffs between multiple networks

ABSTRACT

The disclosure is directed to an access terminal, and method for selecting an access point for handing off the access terminal. The access terminal may include a processor. The processor may be configured to access a list access points and select one of the access points on the list based on the current traffic state of the access terminal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 60/794,042, filed on Apr. 20, 2006, entitled“System Selection and Handoff Design for WLAN 3G Interworking,” which isassigned to the assignee hereof, and the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND

1. Field

The present disclosure relates generally to telecommunications, and moreparticularly, to systems and methods to support the handoff of an accessterminal from one network to another in a wireless communicationssystem.

2. Background

Wireless access terminals can include multiple communication protocols.Recently, access terminals have become multifunctional devices,frequently providing email, Internet access, as well as traditionalcellular communications. Access terminals can be equipped with wide areawireless connectivity utilizing different technologies, such as thirdgeneration wireless or cellular systems (3G), Institute for Electricaland Electronic Engineers (IEEE) 802.16 (WiMax), and other to-be-definedWireless Wide Area Network (WWAN) technologies. Meanwhile, IEEE 802.11based Wireless Local Area Network (WLAN) connectivity is being installedin access terminals as well. On the horizon, ultra-wideband (UWB) and/orBluetooth-based Wireless Personal Area Network (WPAN) local connectivitymay also be available in access terminals

Other examples of multiple communication protocols in an access terminalinclude a laptop computer that may include a WPAN to connect the laptopto a wireless mouse, a wireless keyboard, and the like. In addition, thelaptop computer may include an IEEE 802.11b or 802.11g device to allowthe laptop computer to communicate with a WLAN. WLAN has become popularand, for example, is being set up in homes for both personal andbusiness purposes. In addition, coffee shops, Internet cafes, librariesand public and private organizations utilize WLANs.

WWAN technologies are distinguished by wide area (ubiquitous) coverageand wide area deployment. However, they can suffer from buildingpenetration losses, coverage holes and comparatively, to WLAN and WPAN,limited bandwidth. WLAN and WPAN technologies deliver very high datarates, approaching hundreds of Mbps, but coverage is typically limitedto hundreds of feet in the case of WLAN and tens of feet in the case ofWPAN.

The number of networks and protocols continues to increase rapidly dueto demands for functionality associated with unique user demands anddivergent protocols. Such disparate networks and protocols are laboriousfor a user to switch between and in many cases, the user is trapped in anetwork without regard to what might be the optimal network for the userat a given time. In view of the foregoing, there is a need to providefor seamless transition between networks and/or protocols for optimizingand converging on the best communication protocol for the user.

SUMMARY

An aspect of an access terminal is disclosed. The access terminalincludes a processor configured to access a list access points andselect one of the access points on the list based on the current trafficstate of the access terminal.

An aspect of a method of communications on an access terminal isdisclosed. The method includes accessing a list access points, andselecting one of the access points on the list based on the currenttraffic state of the access terminal.

Another aspect of an access terminal is disclosed. The access terminalincludes means for accessing a list access points, and means forselecting one of the access points on the list based on the currenttraffic state of the access terminal.

An aspect of a computer-readable medium including instructions storedthereon is disclosed. The computer-readable medium includes a firstinstruction set for accessing a list access points, and a secondinstruction set for selecting one of the access points on the list basedon the current traffic state of the access terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of a wireless communications system are illustrated byway of example, and not by way of limitation, in the accompanyingdrawings, wherein:

FIG. 1 is a conceptual block diagram illustrating an example of acommunications system featuring more than one radio access technology;

FIG. 2 is a block diagram illustrating an example of an access terminal;

FIG. 3 is a flow chart illustrating an example of a handoff of an accessterminal to an access point;

FIG. 4 is a flow chart illustrating another example of a handoff of anaccess terminal to an access point; and

FIG. 5 is a functional block diagram illustrating another example of anaccess terminal.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

In the following detailed description, various techniques will bedescribed in connection with a handoff of an access terminal from onenetwork to another. A number of these techniques will be described inthe context of an access terminal traveling through WWAN with one ormore wireless WLANs dispersed throughout the coverage region. Whilethese techniques may be well suited for this application, those skilledin the art will readily appreciate that these techniques can be extendedto other access terminals capable of utilizing different protocols tocommunicate with different networks. By way of example, these techniquesmay be applied to an access terminal capable of switching between aCDMA2000 1x network and a GSM network and a UMTS network. Accordingly,any reference to an access terminal capable of communicating with one ormore WLANs as it moves throughout a WWAN is intended only to illustratevarious aspects of the invention, with the understanding that theseaspects have a wide range of applications.

FIG. 1 is a conceptual block diagram of an embodiment of a wirelesscommunications system 100. An access terminal 102 is communication witha WWAN 104. The access terminal 102 may be a wireless telephone, alaptop computer, a personal digital assistant (PDA), a data transceiver,a pager, a camera, a game console, a modem, or any other suitablewireless communications device. The access terminal 102 may be referredto by those skilled in the art by other names such as a handset, userterminal, user equipment, mobile station, mobile unit, subscriberstation, subscriber unit, mobile radio, radio telephone, wirelessstation, wireless device, wireless communications device, or some otherterminology. The various concepts described throughout this disclosureare intended to apply all wireless communication devices regardless oftheir specific nomenclature.

The WWAN 104 includes a Base Station Controller (BSC) 106 supporting anumber of base station transceivers, or access points, dispersedthroughout the WWAN 104. A single access point 108 is shown in FIG. 1for simplicity of explanation. A Mobile Switching Center (MSC) 110 maybe used to provide an interface to a Public Switched Telephone Network(PSTN) 112, or other circuit-switched network. Although not shown inFIG. 1, the WWAN 104 may employ numerous BSCs each supporting any numberof access points to extend the geographic reach of the WWAN 104. Whenmultiple BSCs are employed, the MSC 110 may also be used to coordinatecommunications between the BSCs.

A Home Location Register (HLR) 114 is shown coupled to the MSC 110, butalternatively may be co-located or integrated with the MSC 110. The HLR114 is a entity that manages access terminals by maintaining a record ofsubscribers to a service provider. It maintains such information as thesubscriber's phone number, authentication data, allowed services,billing information, etc. The HLR 114 is also used to provide subscriberinformation to foreign networks serving the access terminal 102. By wayof example, when the access terminal 102 roams outside its home network,subscriber information located in the HLR 114 may be sent to a VisitorLocation Register VLR (not shown) associated with the MSC currentlyserving the access terminal. The MSC 110 shown in FIG. 1 also maintainsits own VLR 116 to support roaming access terminals from other networks.

One or more WLANs may be dispersed throughout the geographic coverageregion of the WWAN 104. A single WLAN 118 is shown in FIG. 1 forsimplicity of explanation. The WLAN 118 may be an IEEE 802.11 network,or any other suitable network. The WLAN 118 includes a number of accesspoints 120 that connect the access terminal 102 to the Internet 122, orother packet-based network, through a Packet Data Interworking Function(PDIF) 124.

In the communications system 100 shown in FIG. 1, the access terminal102 is capable of communicating over the WWAN 104 using 3G wirelesstechnology. As the access terminal 102 moves into the coverage region ofthe WLAN 118, it may be handed off to an access point 120 andcommunicate over the Internet using Voice over Internet Protocol (VoIP).An IP Multimedia Subsystem (IMS) 126 may be used by the access terminal102 to provide multimedia and voice services controlled by a SessionInitiation Protocol (SIP). SIP is a signaling protocol used over IPnetworks for VoIP.

The IMS 126 includes a Media Gateway (MGW) 128. The MGW 128 terminatesthe encoded voice stream from the PSTN 112 and the voice packets fromthe Internet 122. A Call Session Control function (CSCF) 130communicates with a Home Subscriber Server (HSS) 132. Much like the HLR114 in the WWAN 104, the HSS 132 maintains subscriber information. TheCSCF 130 also determines the routing to the access terminal 102 formobile terminated calls and supports signaling with the access terminal102 for call setup and supplemental services through SIP. A MediaGateway Control Function (MGCF) 136 communicates with CSCF 130 throughSIP to control the MGW 128. The MGCF 136 also provides Signaling SystemNo. 7 (SS7) protocol for call setup over the PSTN 112.

In the communications system 100 shown in FIG. 1, the access terminal102 may use the WWAN 104 to access the PSTN 112 in a conventionalfashion. Once the access terminal 102 is connected to the WWAN 104, itmay choose to either utilize the circuit switched (CS) services offeredby the traditional CS network or utilize the services of the IMS 126through a registration procedure or both. The CS registration procedureinvolves the access terminal 102 as well as elements in CS core such asserving MSC 110, VLR 116, and HLR 114. The CS registration informationcan be conveyed to the VCC AS 134 using protocols such as WirelessIntelligent Network (WIN) or Customized Applications for Mobile EnhancedLogic (CAMEL). The IMS registration procedure begins with the accessterminal 102 sending a SIP registration request to the packet switched(PS) core functions such as the PDIF 124, PDSN (not shown), or SGSN-GGSN(not shown). The request is forwarded by the PS core to the CSCF 130.The CSCF 130 forwards the registration to the Voice Call ContinuityApplication Server (VCC AS) 134. The VCC AS 134 provides an interfacebetween CS core network and IMS core network. The CSCF 130 alsocommunicates with the HSS 132 to obtain the user's profile and completethe registration procedure.

When a user on the access terminal 102 makes a call over the WLAN 118 tothe PSTN 112, SIP signaling is exchanged between the access terminal 102and the CSCF 130. In response, the CSCF 130 selects a MGCF 136 andsignals the MGCF 136 using SIP. The MGCF 136 instructs the MGW 128 toallocate the necessary resources to support the call. The MGCF 136 alsodelivers the SS7 setup messages to the called party through the PSTN112. Once the call is set up, the MGW 128 performs any necessarytranscoding between the media formats used on the Internet 122 and thoseused on the PSTN 112. In the event that the access terminal 102 ishanded off to the WWAN 104 during the call, the necessary signalinginformation related to the call is anchored in the VCC AS 134 where asthe bearer path is anchored in the MGW 128.

FIG. 2 is a simplified block diagram illustrating an example of anaccess terminal 102 capable of supporting both WWAN and WLANcommunications. The access terminal 102 may include a WWAN transceiver202 and WLAN transceiver 204. In at least one embodiment of the accessterminal 102, the WWAN transceiver 202 is capable of supporting cellularor 3G wireless communications with an access point (not shown) employingCode-Division Multiple Access (CDMA), Wideband Code-Division MultipleAccess (WCDMA), Orthogonal Frequency Division Multiple Access (OFDMA),or any other suitable multiple access scheme. The WLAN transceiver 204may be capable of supporting communications with an access point (notshown) using IEEE 802.11, UWB, Bluetooth and/or other relatedtechnologies. The access terminal 102 may employ two transceivers 202,204 as shown in FIG. 2, or alternatively, a single transceiver capableof supporting multiple protocols. The transceivers 202, 204 are shownwith separate antennas 206, 208, respectively, but the transceivers 202,204 could share a single broadband antenna and a fraction of theRF-chain. Those skilled in the art are readily capable of designing theoptimal transceiver for any particular application.

The access terminal 102 is also shown with a processor 210 coupled toboth transceivers 202, 204, however, a separate processor may be usedfor each transceiver in alternative embodiments of the access terminal102. The processor 210 may be implemented with one or more generalpurpose and/or specific application processors. Software programsresiding in non-volatile memory 212 may be used by the general purposeprocessor(s) to control and manage access to the WWAN and WLAN, as wellas provide other communication and processing functions. The processor210 may also support various user interface devices, such as a keypad214 and display 216. The manner in which the processor 208 isimplemented will depend on the particular application and the designconstraints imposed on the overall system. Those skilled in the art willrecognize the interchangeability of hardware, firmware, and softwareconfigurations under these circumstances, and how best to implement thedescribed functionality for each particular application.

In at least one embodiment of the access terminal 102, the processor 210may be configured to maintain certain databases in the non-volatilememory 212, or elsewhere, to provide for seamless transition between theWWAN and the WLAN. By way of example, the processor 210 may create andmaintain a database with a list of access points that have previouslyprovided service to the access terminal 102. This database, referred toas a “Visited AP List,” may include historical information relating tothe quality of service provided by each access point in the past.

It is also possible that this database is stored in network and both theaccess terminal 102 and the network coordinate to manage this database.Such coordination may include a procedure for the network to populatethe database initially or update the database based on the knowledge ofthe access point entries added by the access terminal. Also, the networkcan use the information reported by the access terminal to learn andupdate its knowledge of the topology of available access points thatpotentially belong to another access network.

When the processor 210 initially attempts to associate with an accesspoint for the first time, the access point may be placed on the VisitedAP List. The processor 210 associates with the access point by settingup a wireless connection. Once a wireless connection is established, theprocessor 210 then attempts to establish a network connection to theInternet and complete SIP registration to support VoIP. The success, orfailure, of the processor 210 to establish a wireless and networkconnection, and complete SIP registration, may be recorded in theVisited AP List. The processor 210 may also record in the Visited APList a number of quality metrics relating to the various traffic statesof the access terminal 102.

The processor 210 may add access points to the Visited AP List by theirMAC ID (unique identifier of the access point). For each access pointentry, the processor 210 may include any information that may be usefulto assist it in a handoff between the WWAN and the WLAN, or aninter-access point handoff within the WLAN 118. This information may beupdated by the processor 210 every time it associates with an accesspoint. Examples of access point entries include a MAC ID, a SSID (systemname), a MDID (MAC address of authenticating entity), a Domain ID(common gateway for inter-access point voice call handoff), a NetworkDomain (IP address of the DNS server or IP address of DHCP server andrelated DHCP parameters), a time stamp, an indication as to whether thelast attempt by the access terminal to associate with the access pointwas successful, the number of failed attempts to associate with theaccess point, a weighted ratio of successful associations with theaccess point with the most recent successes given more weight, anindication as to whether the last attempt to establish a networkconnection through the access point was successful (successfulassignment of an IP address from a DHCP server), the number of failedattempts to establish a network connection through the access point, aweighted ratio of successful network connections through the accesspoint with recent successes given more weight, an indication as towhether the last SIP registration was successful, the number of failedSIP registration attempts, the VoIP setup latency through the accesspoint, the quality of the voice call in terms of jitter, delay, lostframes and dropped calls, an indication as to whether quality of service(QoS) is enabled, an indication of the maximum listen interval supportedby the access point, Delivery Traffic Indication Message (DTIM) intervalsupported by the access point (interval between broadcast/multicastmessages), and a WWAN fingerprint (set of access point pilot signalsvisible to the access terminal while associated with the access point).Those skilled in the art will be readily able to determine theappropriate information to include in the Visited AP List depending uponthe particular application.

When the access terminal 102 performs the inter AP handoff, the accessterminal 102 performs 802.11 authentication and association.Additionally, when required by the access network, the terminal mayperform 802.11i/802.1X or WPA authentication. However, when the accessnetwork supports pre-authentication, complete 802.1X authentication maynot be required and thus the handoff latency may be reduced. The accessterminal 102 can store this information regarding which access points doand do not belong to the same authentication domain in the Visited APlist to determine the suitable candidate for handoff. After the accessauthentication, the access terminal 102 uses DHCP to acquire IP address.When there is change in IP address after the inter-AP handoff, theaccess terminal 102 needs to either reestablish or update the VPN withPDIF using IKEv2 or MOBIKE procedure. This VPN establishment procedurefurther introduces delay in handoff procedure. Such delay may not betolerable for real time applications such as VoIP, video telephony, etc.However, not all inter-AP handoff may result in change in IP addressassigned to the access terminal. In particular when the access pointsreside on the same subnet are served by the same DHCP server, the accessterminal will be able to hold on to its IP address. When there is nochange in the IP address of the access terminal, the access terminaldoes not have to perform time-consuming procedure of either VPNestablishment or VPN update. The access terminal will thus record theinformation whether the handoff between a pair of access points resultsin change of IP address or not. Moreover, the access terminal will groupall the access points that retain the IP address assignment together.Such groups can be optionally identified by arbitrary group identifieror other unique attributes such as IP address of the DHCP server tosimplify implementation.

The processor 210 may also be configured to maintain one or moreprovisioned databases in the non-volatile memory 212. By way of example,access terminal 102 may be provisioned with information that allows theprocessor to quickly associate with a preferred access point, orseamlessly handoff a call from the WWAN to a preferred access point.Similar to the Preferred Roaming List (PRL) commonly employed incellular phones, the access terminal 102 may store a list of preferredaccess points, along with the MAC addresses, channel, and securitycredentials for each. A typical application may include a company thatissues access terminals to its employees with company access pointsprovisioned in the access terminal. Another application may include auser with a WLAN in his home. In this application, the user may manuallyprovision in the access terminal the access points located in his home.

The processor 210 may also be configured to maintain a databasecontaining a list of access points that should be avoided. This list mayinclude, by way of example, rogue access points. A rogue access point isan access point that is placed in the vicinity of an access network by amalicious individual in an attempt to disturb the service offered by theaccess network provider. Typically, these rogue access points will notprovide WAN connectivity. The list may also include access points thathave repeatedly failed to provide acceptable service in the past. Anaccess point on the list may be unable to provide acceptable servicebecause of disturbances in the wireless channel, poor networkconnectivity, the inability to quickly handoff the access terminal toanother access point, or for any other reason that would result in lowquality service. Some access points may use local policies such as MACaddress filtering or IP address filtering to prevent some accessterminals from using them, in which case those access points may belisted. The list may also include access points where the accessterminal failed to get an IP address. The list may also include accesspoints where the access terminal failed to authenticate and set up asecure link even though the appropriate credentials were available. Someaccess points in the list may feature a poor implementation that makesthem unsuitable for a given type of service (VoIP).

The processor 210 may maintain a database in volatile memory (notshown), or elsewhere, containing a list of candidate access points forhanding off the access terminal 102. This list is referred to as a“Candidate AP List.” During operation, the processor 210 periodicallyscans the WLAN for access points using a passive or active scan. Theprocessor 210 adds each access point discovered during the scan to theCandidate AP List. Accompanying each access point entry is a MAC ID, aSSID, a MDID, a Domain ID, a Network Domain, and a time stamp. Theprocessor 210 may also include the number of active or passive scans inwhich the access point was missed (i.e., missing probe response orbeacons). The access point may be deleted from the Candidate AP List ifthere are too many missed scans or missed beacons.

The information from the Visited AP List may be used to control certainquality variables for each access point in the Candidate AP List. Morespecifically, the information in the Visited AP List may be used tocontrol an “association variable” that indicates the likelihood ofsuccess that the access terminal will be able to associate with theaccess point. The information in the Visited AP List may also be used tocontrol a “network variable” and a “SIP registration variable” thatrespectively indicate the likelihood of success that the access terminalwill be able to establish a network connection and complete SIPregistration through the access point.

Each access point in the Candidate AP List may also include a handoffflag for each traffic state. The handoff flag may be enabled or disabledbased on the quality variables and the information in the Visited APList. By way of example, the Candidate AP List may include a idlehandoff flag for each access point. The idle handoff flag may be enabledif the association, network and SIP registration variables are abovecertain thresholds. These thresholds may be set conservatively (i.e.,low) because idle handoffs may be attempted even if the likelihood ofsuccess is low.

A data session handoff flag may also be included for each access pointon the Candidate AP List. More aggressive thresholds (i.e., higher) maybe required to enable the data session handoff flag for the associationand network variables. However, a data session handoff may be attemptedeven if the likelihood of successfully completing SIP registration islow. Therefore, the threshold for the SIP registration variable canremain conservative.

The Candidate AP List may also include a voice call handoff flag foreach access point. Enablement of the voice call handoff flags mayrequire aggressive thresholds for the association, network and SIPregistration variables. In addition, historical information from theVisited AP List relating to the voice call quality and VoIP setuplatency should also be considered when determining whether to enable thevoice call handoff flag. Various metrics may be used to determine thevoice quality of each call through an access point including, by way ofexample, delay, jitter, frame loss and dropped calls. The handoff of avoice call to an access point should be attempted only when the accesspoint has demonstrated a history of providing acceptable voice quality.

An inter-access point voice call handoff flag may also be included foreach access point. Enablement of the inter-access voice call handoffflag should require aggressive thresholds for the association, network,and SIP registration variable, good voice quality and low VoIP setuplatency. In addition, a handoff should be attempted only where the voicecall can be continued using the same IP address. The Domain ID in theCandidate AP List may be consulted to ensure this condition is metbefore enabling this flag.

The candidate AP list may also include an indication as to whether QoSis enabled, the received signal strength indicator (RSSI) of the proberesponse or beacon of the access point the duration with RSSI above agiven threshold, the beacon interval of the access point, the timesynchronization function (TSF) offset, and any other information thatmight be useful to the processor 210 for providing seamless transitionsto access points.

The processor 210 may also maintain a database in volatile memory (notshown), or elsewhere, a “WWAN Candidate List.” The WWAN Candidate Listis created by the processor 210 from periodic scans for access points inthe WWAN. The list may also be refreshed by observing the RSSI of anyframe received from that access point. The WWAN Candidate List includesa predetermined number of candidate access points having the strongestpilot signals.

Various handoff procedures may be implemented by the processor 210. Inat least one embodiment, the processor 210 may perform a reactive orproactive handoff from the WWAN to the WLAN. A reactive handoff occurswhen the processor 210 determines that a serving access point in theWWAN has poor signal quality or is providing poor data service, whichmight be the case if the access terminal is moving away from the servingaccess point. If this occurs, the processor 210 selects the access pointwith the strongest RSSI in the Candidate AP List with an enabled handoffflag indicating that the access point can support the current trafficstate of the access terminal 102 (i.e., idle, data session, voice call).

A proactive handoff involves the handoff of the access terminal 102 tothe WLAN access point having the highest RSSI in the Candidate AP Listwith an enabled handoff flag for the current traffic state of the accessterminal 102, provided the RSSI is above a threshold for a sustainedperiod of time. If multiple access points in the WLAN have comparableRSSIs and the appropriate handoff flag enabled, the processor 210 mayhandoff the access terminal 102 to an access point with QoS enabled anda lesser load. In the idle state, the processor 210 may also initiate aproactive handoff if camping on the WLAN is the preferred mode ofoperation.

A proactive handoff may also be user initiated. A user on an accessterminal 102 served by the WWAN may initiate a handoff to a WLAN accesspoint by making a keypad entry. This might occur, for example, when auser enters his home or a hotspot equipped with a WLAN.

When the access terminal 102 is associated with an access point in theWLAN, the processor 210 may perform an inter-access point handoff, orhandoff the access terminal 102 to the WWAN. In at least one embodimentof the processor 210, the processor 210 may perform a reactive orproactive inter-access point handoff, but only a reactive handoff to anaccess point in the WWAN.

A proactive inter-access point handoff may be performed in each trafficstate. During a voice call, for example, the processor 210 mayperiodically search for an access point in the Candidate AP List thatcan support an inter-access point handoff for a voice call (i.e., anenabled inter-access point voice call handoff flag) and has a RSSI that(1) exceeds the RSSI of the serving access point by some threshold, and(2) has enough resources left to support an additional voice call. Ifthe processor 210 is able to locate an access point in the Candidate APList that satisfies this criteria, it hands off the access terminal 102to that access point. If the processor 210 finds multiple access pointsin the Candidate AP List that satisfy this criteria, the processor 210then selects an access point with QoS enabled for handoff of the accessterminal 102.

During a data session, or when the access terminal 102 is idle, aproactive inter-access point handoff may be performed by the processor210 by periodically searching the Candidate AP List for an access pointthat can support the current traffic state (i.e., an enabled idle ordata session handoff flag), and has a RSSI that (1) exceeds the RSSI ofthe serving access point by some threshold, and (2) is sufficient tosupport the current traffic state. If the processor 210 is able tolocate an access point in the Candidate AP List that satisfies thiscriteria, it hands off the access terminal 102 to this access point. Ifthe processor 210 find multiple access points in the Candidate AP Listthat satisfy this criteria, the processor 210 then selects an accesspoint with QoS enable for handoff of the access terminal 102.

A reactive handoff may result in an inter-access point handoff, or ahandoff of the access terminal 102 to the WWAN. During a voice call, ifthe RSSI of the serving access point falls below a threshold, theprocessor 210 handoffs the access terminal 102 to the WWAN if it canfind an access point in the WWAN Candidate List with a pilot signalstrength that exceeds a certain threshold. If the processor 210 isunable to find a suitable access point in the WWAN, then it will attemptan inter-access point handoff to a WLAN access point in the Candidate APList that can support an inter-access point handoff of a voice call(i.e., an enabled inter-access point voice call handoff flag) and has aRSSI sufficient to support a voice call with acceptable quality. Again,if the processor 210 finds multiple access points that satisfy thiscriteria, the processor 210 then selects an access point with QoSenabled for handoff of the access terminal 102.

During a data session, or when the access terminal 102 is idle, areactive handoff may be initiated by the processor 210 if the RSSI ofthe serving access point falls below a certain threshold. If thiscondition exists, the processor 210 then initiates a handoff to the WWANif it can find an access point in the WWAN Candidate List with a pilotsignal strength that exceeds a certain threshold. If the processor 210is unable to find a suitable access point in the WWAN, then it willattempt an inter-access point handoff to the access point in theCandidate AP List with the highest RSSI that can support the currenttraffic state (i.e., an enabled idle or data session handoff flag).Again, if the processor 210 finds multiple access points that satisfythis criteria, the processor 210 then selects an access point with QoSenable for handoff of the access terminal 102.

In at least one embodiment of the access terminal, the user can initiatea handoff between the WWAN and WLAN or an inter-access point handoff ineach traffic state. In each case, the available access points in theCandidate AP List or WWAN Candidate List can be presented to the user onthe display 216 of the access terminal. The user can then make one ormore entries on the keypad 214 to select an access point for handoff.

FIG. 3 is a simplified flow diagram illustrating the handoff of theaccess terminal to an access point in the WLAN. The handoff may be aninter-access point handoff, or alternatively, a handoff from an accesspoint in the WWAN. Referring to FIG. 3, the access terminal is operatingin one of several traffic states (i.e., voice call, data session, idlemode) in step 302. In step 304, the processor in the access terminalsearches through the Candidate AP List for a target access point. Thesearch for a target access point may be in support of a reactive orproactive handoff and the criteria used to select the target accesspoint may be based on the current traffic state of the access terminal.Once the processor selects a target access point, it attempts to handoff the access terminal to the target in step 306. The success, orfailure, of the handoff is recorded by the processor in the Visited APList in step 308. Assuming that the processor successfully hands off ofthe access terminal, the processor also records in the Visited AP Listvarious quality metrics for the target access point based on the currenttraffic state of the access terminal. Once the Visited AP List isupdated, the access terminal continues to operate through the targetaccess point in its current traffic state in step 302.

In step 310, the processor performs an active or passive scan for accesspoints. The scan may be periodic or triggered. The periodic scaninterval may vary depending on the current traffic state of the accessterminal and the contents of the Candidate AP List. The results of thescan are filtered by the Visited AP List in step 312. More specifically,the association, network, and SIP registration variables may be computedby the processor from the Visited AP List for each access pointdiscovered during the scan. The variables, along with other qualitymetrics recorded in the Visited AP List, may be used to set the trafficstate handoff flags for each access point. In step 314, the accesspoints are added to the Candidate AP List. The variables, flags, andother information computed from the Visited AP List, may also be addedto the Candidate AP List for each access point entry. Once the CandidateAP List is updated, the access terminal continues to operate in itscurrent traffic state in step 302.

FIG. 4 is a flow chart illustrating another example of a process forselecting an access point. In step 402, the access terminal accesses alist access points. The list may be maintained in a database in theaccess terminal or elsewhere. In step 404, the access terminal selectsone of the access points on the list based on the current traffic stateof the access terminal. The selection of the access point may include aperiodic scan having an interval that depends on the current trafficstate of the access terminal.

In step 406, the access terminal accesses a second list containinginformation regarding access points that have previously served theaccess terminal. In step 408, the access terminal updates theinformation related to the selected one of the access points. Theupdated information may relate to whether the access terminal is able toassociate with the selected one of the access points, the quality ofservice provided by the selected one of the access points, or otherinformation. The quality of service may include delay, jitter, packetloss rate, time taken to associate with the selected one of the accesspoints, dropped frames, or other quality indicators.

In one configuration of the access terminal, the selection of the accesspoint in step 404 may be based on indicators derived from information ina second list regarding access points that have previously served theaccess terminal. The indicators may indicate whether each access pointis a handoff candidate for each traffic state. The information fromwhich the indicators are derived may relate to the quality of serviceprovided to the access terminal by access points that have previouslyserved the access terminal, access points that belong to the same subnetserved by the same dynamic host configuration protocol (DHCP), accesspoints that belong to the same authentication domain, etc.

The selection of the access point may also be based on real timemeasurements of the access points. The real time measurements includereceived power from the access points, loading on the access points, andinterference on the channel of each of the access points.

The selection of the access point may also be based on a second list ofaccess points that the access terminal is prohibited from associatingwith.

The selection of the access point may further be based on a list ofpreferred access points.

In step 410, the access terminal is handed off to the selected accesspoint. The handoff of the access point may be between two access pointsin the same network or different networks. The access terminal willsearch for access points in the WLAN before searching for access pointsin the cellular network when the access terminal is in a data session.The access terminal will search for access points in the cellularnetwork before searching for access points in the WLAN when the accessterminal is in a voice call.

FIG. 5 is a functional block diagram of an access terminal. The accessterminal 102 includes a module 502 for accessing a list access points.The list may be maintained in a database in the access terminal orelsewhere. The access terminal 102 also includes a module 504 forselecting one of the access points on the list based on the currenttraffic state of the access terminal. The selection of the access pointmay include a periodic scan having an interval that depends on thecurrent traffic state of the access terminal.

The access terminal 102 includes a module 506 for accessing a secondlist containing information regarding access points that have previouslyserved the access terminal. The access terminal 102 also includes amodule 508 for updating the information related to the selected one ofthe access points. The updated information may relate to whether theaccess terminal is able to associate with the selected one of the accesspoints, the quality of service provided by the selected one of theaccess points, or other information. The quality of service may includedelay, jitter, packet loss rate, time taken to associate with theselected one of the access points, dropped frames, or other qualityindicators.

In one configuration of the access terminal 102, the module 504 mayselect an access point based on indicators derived from information in asecond list regarding access points that have previously served theaccess terminal. The indicators may indicate whether each access pointis a handoff candidate for each traffic state. The information fromwhich the indicators are derived may relate to the quality of serviceprovided to the access terminal by access points that have previouslyserved the access terminal, access points that belong to the same subnetserved by the same dynamic host configuration protocol (DHCP), accesspoints that belong to the same authentication domain, etc.

The selection of the access point by the module 504 may also be based onreal time measurements of the access points. The real time measurementsinclude received power from the access points, loading on the accesspoints, and interference on the channel of each of the access points.

The selection of the access point by the module 504 may also be based ona second list of access points that the access terminal is prohibitedfrom associating with.

The selection of the access point by the module 504 may further be basedon a list of preferred access points.

The access terminal 102 includes a module 510 for handing off to theselected access point. The handoff of the access point may be betweentwo access points in the same network or different networks. The accessterminal will search for access points in the WLAN before searching foraccess points in the cellular network when the access terminal is in adata session. The access terminal will search for access points in thecellular network before searching for access points in the WLAN when theaccess terminal is in a voice call.

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an example of exemplary approaches. Based upondesign preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged while remainingwithin the scope of the present disclosure. The accompanying methodclaims present elements of the various steps in a sample order, and arenot meant to be limited to the specific order or hierarchy presented.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the embodiments disclosed herein may be implemented aselectronic hardware, computer software, or combinations of both. Toclearly illustrate this interchangeability of hardware and software,various illustrative components, blocks, modules, circuits, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present disclosure.

The various illustrative logical blocks, modules, circuits, elements,and/or components described in connection with the embodiments disclosedherein may be implemented or performed with a general purpose processor,a digital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic component, discrete gate or transistor logic,discrete hardware components, or any combination thereof designed toperform the functions described herein. A general-purpose processor maybe a microprocessor, but in the alternative, the processor may be anyconventional processor, controller, microcontroller, or state machine. Aprocessor may also be implemented as a combination of computingcomponents, e.g., a combination of a DSP and a microprocessor, aplurality of microprocessors, one or more microprocessors in conjunctionwith a DSP core, or any other such configuration.

The methods or algorithms described in connection with the embodimentsdisclosed herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. A storagemedium may be coupled to the processor such that the processor can readinformation from, and write information to, the storage medium. In thealternative, the storage medium may be integral to the processor.

The previous description is provided to enable any person skilled in theart to practice the various embodiments described herein. Variousmodifications to these embodiments will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other embodiments. Thus, the claims are not intended to belimited to the embodiments shown herein, but is to be accorded the fullscope consistent with the language claims, wherein reference to anelement in the singular is not intended to mean “one and only one”unless specifically so stated, but rather “one or more.” All structuraland functional equivalents to the elements of the various embodimentsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. No claim element is to be construed under the provisions of35 U.S.C. §112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for” or, in the case of a method claim, theelement is recited using the phrase “step for.”

1. An access terminal, comprising: a processor configured to access alist of access points and select one of the access points on the listbased on the current traffic state of the access terminal.
 2. The accessterminal of claim 1, wherein the processor is further configured tomaintain a database in the access terminal, the database comprising thelist of access terminals.
 3. The access terminal of claim 1, wherein theprocessor is further configured to access a second list containinginformation regarding access points that have previously served theaccess terminal, the processor being further configured to update theinformation related to the selected one of the access points.
 4. Theaccess terminal of claim 3, wherein the updated information relates towhether the access terminal is able to associate with the selected oneof the access points.
 5. The access terminal of claim 3, wherein theinformation relates to the quality of service provided by the selectedone of the access points to the access terminal.
 6. The access terminalof claim 5, wherein the quality of service includes delay, jitter,packet loss rate, or time taken to associate with the selected one ofthe access points.
 7. The access terminal of claim 5, wherein thequality of service includes dropped frames.
 8. The access terminal ofclaim 7, wherein the quality of service includes dropped frames betweenthe access terminal and the far end connection.
 9. The access terminalof claim 1, wherein the processor is further configured to access asecond list containing information regarding access points that havepreviously served the access terminal, the processor being furtherconfigured to maintain indicators for one or more of the access pointson the list from the information on the second list, the selection ofsaid one of the access points also being based on the indicators. 10.The access terminal of claim 9, wherein the indicators for each of oneor more access points indicates whether the access point is a handoffcandidate for each traffic state, and wherein the processor is furtherconfigured to control the state of the indicators based on theinformation on the second list.
 11. The access terminal of claim 9,wherein the information on the second list includes historicalinformation relating to the quality of service provided to the accessterminal by one or more access points that have previously served theaccess terminal.
 12. The access terminal of claim 9, wherein theinformation on the second list identifies the access points that belongto the same subnet served by the same dynamic host configurationprotocol (DHCP).
 13. The access terminal of claim 9, wherein theinformation on the second list identifies access points that belong tothe same authentication domain.
 14. The access terminal of claim 1,wherein the processor is further configured to handoff the accessterminal from a serving access point in a first network to the selectedone of the access points, the selected one of the access points being ina second network.
 15. The access terminal of claim 1, wherein theprocessor is further configured to handoff the access terminal from aserving access point in a network to the selected one of the accesspoints, the selected one of the access points being in the same networkas the serving access point.
 16. The access terminal of claim 1, whereinthe processor is further configured to select one of the access pointson the list by performing a periodic scan having an interval thatdepends on the current traffic state of the access terminal.
 17. Theaccess terminal of claim 1, wherein the selection of said one of theselected access points by processor is also based on real timemeasurements of the access points on the list.
 18. The access terminalof claim 17, wherein the real time measurements include received powerfrom the access points, loading on the access points, and interferenceon the channel of each of the access points.
 19. The access terminal ofclaim 1, wherein the processor is further configured to access a secondlist of access points that the access terminal is prohibited fromassociating with, the selection of said one of the access points alsobeing based on the second list.
 20. The access terminal of claim 1,wherein the processor is further configured to access a list ofpreferred access points, the selection of said one of the access pointsalso being based on the list of preferred access points.
 21. The accessterminal of claim 1, wherein the access points on the list are from awireless local area network (WLAN) and a cellular network, and whereinthe processor is further configured to select said one of the accesspoints by searching for access points in the WLAN before searching foraccess points in the cellular network when the access terminal is in adata session.
 22. The access terminal of claim 1, wherein the accesspoints on the list are from a wireless local area network (WLAN) and acellular network, and wherein the processor is further configured toselect said one of the access points by searching for access points inthe cellular network before searching for access points in the WLAN whenthe access terminal is in a voice call.
 23. A method of communicationson an access terminal, comprising: accessing a list access points; andselecting one of the access points on the list based on the currenttraffic state of the access terminal.
 24. The method of claim 23,further comprising maintaining a database in the access terminal, thedatabase comprising the list of access terminals.
 25. The method ofclaim 23, further comprising accessing a second list containinginformation regarding access points that have previously served theaccess terminal, and updating the information related to the selectedone of the access points.
 26. The method of claim 25, wherein theupdated information relates to whether the access terminal is able toassociate with the selected one of the access points.
 27. The method ofclaim 25, wherein the information relates to the quality of serviceprovided by the selected one of the access points to the accessterminal.
 28. The method of claim 27, wherein the quality of serviceincludes delay, jitter, packet loss rate, or time taken to associatewith the selected one of the access points.
 29. The method of claim 27,wherein the quality of service includes dropped frames.
 30. The methodof claim 29, wherein the quality of service includes dropped framesbetween the access terminal and the far end connection.
 31. The methodof claim 23, further comprising accessing a second list containinginformation regarding access points that have previously served theaccess terminal, and maintaining indicators for one or more of theaccess points on the list from the information on the second list, theselection of said one of the access points also being based on theindicators.
 32. The method of claim 31, wherein the indicators for eachof one or more access points indicates whether the access point is ahandoff candidate for each traffic state, the method further comprisingcontrolling the state of the indicators based on the information on thesecond list.
 33. The method of claim 31, wherein the information on thesecond list includes historical information relating to the quality ofservice provided to the access terminal by one or more access pointsthat have previously served the access terminal.
 34. The method of claim31, wherein the information on the second list identifies the accesspoints that belong to the same subnet served by the same dynamic hostconfiguration protocol (DHCP).
 35. The method of claim 31, wherein theinformation on the second list identifies access points that belong tothe same authentication domain.
 36. The method of claim 23, furthercomprising handing off the access terminal from a serving access pointin a first network to the selected one of the access points, theselected one of the access points being in a second network.
 37. Themethod of claim 23, further comprising handing off the access terminalfrom a serving access point in a network to the selected one of theaccess points, the selected one of the access points being in the samenetwork as the serving access point.
 38. The method of claim 23, whereinthe selection of said one of the access points comprising performing aperiodic scan having an interval that depends on the current trafficstate of the access terminal.
 39. The method of claim 23, wherein theselection of said one of the selected access points is also based onreal time measurements of the access points on the list.
 40. The methodof claim 39, wherein the real time measurements include received powerfrom the access points, loading on the access points, and interferenceon the channel of each of the access points.
 41. The method of claim 23,further comprising accessing a second list of access points that theaccess terminal is prohibited from associating with, the selection ofsaid one of the access points also being based on the second list. 42.The method of claim 23, further comprising accessing a list of preferredaccess points, the selection of said one of the access points also beingbased on the list of preferred access points.
 43. The method of claim23, wherein the access points on the list are from a wireless local areanetwork (WLAN) and a cellular network, and wherein the selection of saidone of the access points comprises searching for access points in theWLAN before searching for access points in the cellular network when theaccess terminal is in a data session.
 44. The method of claim 23,wherein the access points on the list are from a wireless local areanetwork (WLAN) and a cellular network, and wherein the selection of saidone of the access points comprises searching for access points in thecellular network before searching for access points in the WLAN when theaccess terminal is in a voice call.
 45. An access terminal, comprising:means for accessing a list access points; and means for selecting one ofthe access points on the list based on the current traffic state of theaccess terminal.
 46. The access terminal of claim 45, further comprisingmeans for maintaining a database in the access terminal, the databasecomprising the list of access terminals.
 47. The access terminal ofclaim 45, further comprising means for accessing a second listcontaining information regarding access points that have previouslyserved the access terminal, and means for updating the informationrelated to the selected one of the access points.
 48. The accessterminal of claim 47, wherein the updated information relates to whetherthe access terminal is able to associate with the selected one of theaccess points.
 49. The access terminal of claim 47, wherein theinformation relates to the quality of service provided by the selectedone of the access points to the access terminal.
 50. The access terminalof claim 49, wherein the quality of service includes delay, jitter,packet loss rate, or time taken to associate with the selected one ofthe access points.
 51. The access terminal of claim 49, wherein thequality of service includes dropped frames.
 52. The access terminal ofclaim 51, wherein the quality of service includes dropped frames betweenthe access terminal and the far end connection.
 53. The access terminalof claim 45, further comprising means for accessing a second listcontaining information regarding access points that have previouslyserved the access terminal, and means for maintaining indicators for oneor more of the access points on the list from the information on thesecond list, and wherein the means for selecting one of the accesspoints on the list is configured to use the indicators to select saidone of the access points.
 54. The access terminal of claim 53, whereinthe indicators for each of one or more access points indicates whetherthe access point is a handoff candidate for each traffic state, theaccess terminal further comprising means for controlling the state ofthe indicators based on the information on the second list.
 55. Theaccess terminal of claim 53, wherein the information on the second listincludes historical information relating to the quality of serviceprovided to the access terminal by one or more access points that havepreviously served the access terminal.
 56. The access terminal of claim53, wherein the information on the second list identifies the accesspoints that belong to the same subnet served by the same dynamic hostconfiguration protocol (DHCP).
 57. The access terminal of claim 53,wherein the information on the second list identifies access points thatbelong to the same authentication domain.
 58. The access terminal ofclaim 45, further comprising means for handing off the access terminalfrom a serving access point in a first network to the selected one ofthe access points, the selected one of the access points being in asecond network.
 59. The access terminal of claim 45, further comprisinghanding off the access terminal from a serving access point in a networkto the selected one of the access points, the selected one of the accesspoints being in the same network as the serving access point.
 60. Theaccess terminal of claim 45, wherein the means for selecting one of theaccess points further comprises means for performing a periodic scanhaving an interval that depends on the current traffic state of theaccess terminal.
 61. The access terminal of claim 45, wherein the meansfor selecting one of the access points is configured to use real timemeasurements to select said on of the access points.
 62. The accessterminal of claim 61, wherein the real time measurements includereceived power from the access points, loading on the access points, andinterference on the channel of each of the access points.
 63. The accessterminal of claim 45, further comprising means for accessing a secondlist of access points that the access terminal is prohibited fromassociating with, wherein the means for selecting one of the accesspoints is configured to use the second list to select said one of theaccess points.
 64. The access terminal of claim 45, further comprisingmeans for accessing a list of preferred access points, wherein the meansfor selecting one of the access points is configured to use the list ofpreferred access points to select said one of the access points.
 65. Theaccess terminal of claim 45, wherein the access points on the list arefrom a wireless local area network (WLAN) and a cellular network, andwherein the means for selecting one of the access points is configuredto search for access points in the WLAN before searching for accesspoints in the cellular network when the access terminal is in a datasession.
 66. The access terminal of claim 45, wherein the access pointson the list are from a wireless local area network (WLAN) and a cellularnetwork, and wherein the means for selecting one of the access points isconfigured to search for access points in the cellular network beforesearching for access points in the WLAN when the access terminal is in avoice call.
 67. A computer-readable medium including instructions storedthereon, comprising: a first instruction set for accessing a list accesspoints; and a second instruction set for selecting one of the accesspoints on the list based on the current traffic state of the accessterminal.
 68. The computer-readable medium of claim 67, furthercomprising a third instruction set for maintaining a database in theaccess terminal, the database comprising the list of access terminals.69. The computer-readable medium of claim 67, further comprising a thirdinstruction set for accessing a second list containing informationregarding access points that have previously served the access terminal,and a fourth instruction set for updating the information related to theselected one of the access points.
 70. The computer-readable medium ofclaim 69, wherein the updated information relates to whether the accessterminal is able to associate with the selected one of the accesspoints.
 71. The computer-readable medium of claim 69, wherein theinformation relates to the quality of service provided by the selectedone of the access points to the access terminal.
 72. Thecomputer-readable medium of claim 71, wherein the quality of serviceincludes delay, jitter, packet loss rate, or time taken to associatewith the selected one of the access points.
 73. The computer-readablemedium of claim 71, wherein the quality of service includes droppedframes.
 74. The computer-readable medium of claim 73, wherein thequality of service includes dropped frames between the access terminaland the far end connection.
 75. The computer-readable medium of claim67, further comprising a third instruction set for accessing a secondlist containing information regarding access points that have previouslyserved the access terminal, and a fourth instruction set for maintainingindicators for one or more of the access points on the list from theinformation on the second list, and wherein the second instruction setis configured to use the indicators to select said one of the accesspoints.
 76. The computer-readable medium of claim 75, wherein theindicators for each of one or more access points indicates whether theaccess point is a handoff candidate for each traffic state, thecomputer-readable medium further comprising a fifth instruction set forcontrolling the state of the indicators based on the information on thesecond list.
 77. The computer-readable medium of claim 75, wherein theinformation on the second list includes historical information relatingto the quality of service provided to the access terminal by one or moreaccess points that have previously served the access terminal.
 78. Thecomputer-readable medium of claim 75, wherein the information on thesecond list identifies the access points that belong to the same subnetserved by the same dynamic host configuration protocol (DHCP).
 79. Thecomputer-readable medium of claim 75, wherein the information on thesecond list identifies access points that belong to the sameauthentication domain.
 80. The computer-readable medium of claim 67,further comprising a third instruction set for handing off the accessterminal from a serving access point in a first network to the selectedone of the access points, the selected one of the access points being ina second network.
 81. The computer-readable medium of claim 67, furthercomprising a third instruction set for handing off the access terminalfrom a serving access point in a network to the selected one of theaccess points, the selected one of the access points being in the samenetwork as the serving access point.
 82. The computer-readable medium ofclaim 67, wherein the second instruction set is configured to perform aperiodic scan having an interval that depends on the current trafficstate of the access terminal.
 83. The computer-readable medium of claim67, wherein the second instruction set is configured to use real timemeasurements to select said on of the access points.
 84. The accessterminal of claim 83, wherein the real time measurements includereceived power from the access points, loading on the access points, andinterference on the channel of each of the access points.
 85. Thecomputer-readable medium of claim 67, further comprising a thirdinstruction set for accessing a second list of access points that theaccess terminal is prohibited from associating with, wherein the secondinstruction set is configured to use the second list to select said oneof the access points.
 86. The computer-readable medium of claim 67,further comprising a third instruction set for accessing a list ofpreferred access points, wherein the second instruction set isconfigured to use the list of preferred access points to select said oneof the access points.
 87. The computer-readable medium of claim 67,wherein the access points on the list are from a wireless local areanetwork (WLAN) and a cellular network, and wherein the secondinstruction set is configured to search for access points in the WLANbefore searching for access points in the cellular network when theaccess terminal is in a data session.
 88. The computer-readable mediumof claim 67, wherein the access points on the list are from a wirelesslocal area network (WLAN) and a cellular network, and wherein the secondinstruction set is configured to search for access points in thecellular network before searching for access points in the WLAN when theaccess terminal is in a voice call.